Hi Molly, welcome to the forums.
I would absolutely NOT use that as a criteria as to whether or not you join as army or air. People your height have been successful, folks 6'5" have probably failed. It's all about preparation and attitude.
A big part of joining the CAF should be to challenge yourself to get outside of your comfort zones, mentally and physically; to do things that you never thought were possible.
So, if you have your heart set on a trade that is army, then go for it. You will have lots of PT on basic to help you on the way to being successful.